Pulse Jet Motorcycle

A first-hand look at a pulse jet motorcycle

Event Report 20150327

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The Experience

I met Tim through a long-time buddy of mine, Kai.  Tim is a jet turbine engineer and used a CAD/simulation program to design a valveless pulse jet engine.  He described its operation during an off-road trip last year, but I had never seen the engine in operation.  But a test run was being conducted in Borrego Springs, so we loaded up Thor and headed to watch.  The engine has  been mounted to an old motorcycle frame and attached to a 30lb propane bottle in preparation for a test run.  We had trouble getting it started due to low fuel, but once a new bottle was attached, it started right up.  There is a link to a youtube posting about 1/2 way down in this page.

The photos below are what we saw.

The boys examine the mechanical monstrosity called the rocket bike.  The engine has to be mounted well aft of the operator due to the intense heat generated during operation.  The whole setup is "hillbilly deluxe", but it DOES work.  The engineering design that went into the engine was impressive, almost as impressive as the effort put into the seat.

The Jedness of the setup is confirmed by looking at the deluxe operator seat.  Thor is visible in the top right of the photo above.

During a previous run, the mounting bracket on the engine broke on rough ground and the engine fell onto the rear fender and melted the sheet metal!

Note the fine heat shield on the fuel line.  The line comes from the tank, through the shield and then wraps around the engine to allow the liquid propane to vaporize before being released into the combustion chamber.  The line goes from standard rubber propane hose to copper tubing to aircraft grade stainless steel tube for the entry into the engine.  The whole assembly is firmly attached to the high-quality frame using baling wire.  The high-tech aircraft-quality stainless steel and TIG-welded engine provides a nice juxtaposition to the scrap-heap construction of the support components!  Nothing says "quality" like baling wire, but there is a good reason for this approach.  During operation, the engine expands in length due to the intense heat and the expansion would break any hard mount points.  So, the engine is only attached on the front end via the bracket and then sits on a cradle on the rear.  The baling wire is only to keep the engine from bouncing out of the cradle during bumps.  Due to the length of the machine, the engine has to be removed during transport to allow it to fit on Kai's trailer.

The propane tank is upside down to allow liquid propane to flow in the pipe (as opposed to the normal vapor for a camp stove or BBQ).  The flow control is a needle valve attached to the original motor mount.  The whole setup is robustly secured with a bungee cord which is not only colorful, but cost effective.

A regular spark plug is used to get the combustion started.  The wires must be removed after ignition because the intense heat will melt the insulation and wires.  The engine is made from special high-temperature stainless steel because regular steel will sag and melt.

The resonance in the engine is initiated with a leaf blower or compressed air.

It is getting dark, almost time for a run!

Kathleen, a certified observer, notes the position of the spark plug and its similarity to certain anatomical features, only smaller (or at least hopefully).

This is a frame-grab from video and since it was really dark it has plenty of motion blur.  But, you can see the heat generated from the engine during operation.  The noise is truly daunting and it was good that I had my ear plugs with me.

Above, the bike returns after a run and is preparing to shut down the engine.  Note the infrared illumination on the ground due to the intense heat of the engine.
A video of the run is available on youtube here.  

Next morning we got a chance to inspect some of the antique equipment in Dan's yard.

There were ocotillos blooming across the road.

A view of the San Filipe Valley on the way back to San Diego.

Yucca cactus in bloom near Banner, CA.

The yucca blooms had an interesting odor; not good or bad, but interesting.

The pulse jet was impressive.  The noise was daunting but the heat glow after dark was awesome, something that has to be experienced in person.

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